Ultra high frequency receiver



A Aug. 8, 1950 E RQY APKER 2,518,113

ULTRA HIGH FREQUENCY RECEIVER Filed June 23, 1945 LOCAL `(SCZILLATOR. 8T-` .I. O` 'y g `fa gfz LOCAL OSCILLATOR.

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by /vWfJW/f@ t-iis 'Attorney afented ug. 8,

UL'rirA nien ritEQUEncY RECEIVER Le- Roy Apker,v Niskayuna, N. Y.,assgnor to General- Electric Company, ar corporation of New York f,

Y Application June 23, 1945, Serial No. 601,124 1 The usual wide bandultra high frequency receiver for spectrum analysis is of thesuperheterodyne type and provides frequency conversion in the firststage of the receiver. It is a characteristic of such a receiverthatffor each single-frequency signal applied to the input, responsesare found when the receiver yis tuned not only to the signal frequencybut also to various other vfrequencies.A The number` and exact values`or positions in the frequency'spectrum of these responses depend on thespecific values of the structuralv components of the receiver.-The-usual receiver of this type has two (the signal land its image) andfrequently has several other responses for each incident frequency, sothat-it' is'often difficult to discriminate betweenAgenuine-andfspurious responses. vAccordingly, it'is'an'objectfof thepresent invention to provide a new and` improved Wide band ultra highfrequency spectrum analyzer for determining the characteristics of areceived wave and in which, over any? practical range of received signalfrequencies, spurious -responsesin the output are minimized.

' It is another object ef my invention toprovide a new and' improvedwide band yultra high fre;- L

quency `signal vconverterv which -is both simple in construction'andreliable -in operation. The converter minimizes spuriousv responses overa wide range of frequency without requiring tuning ele-y ments resonantyin this range. v'In thisway, the

usual ltuners placedi'ahead' of superheterodyne output of the first`stage-"of conversion toremove undesired modulation products. The signalproduced at the 'output ofthe second stage is of' a constantfrequency'having'a value such that it: Etconventional amplifier cir-Acan be amplied muiv, v

' The featuresof-the invention which 1 desire to protect hereinarepointe'd outwith partioularty claims. (o1. 25o- 20) ,2 y n in theappended claims. "The invention itself, together with further objectsand 'advantages thereof, may best be understood by reference to thefollowing description takenin'fconnection with the accompanyingdrawing-in which Fig. l is a block diagramv illustrating the componentparts of an ultra high frequencyl receiver suit# ably embodying myinvention; Fig. 2 isv a horizontal section of my ultra high frequencyappa-L' ratus; Fig. 3 is a vertical sectionl taken along the linev 3-3of Fig; 2; and Fig. 4 is 'an enlarged transverse section-taken along theline 4`'41-of Y Eig. 2.

Y The receiver circuit in Fig.' 1 comprises-a source of input signals lwhich may beg'for-example signals received by? an atenna'fand variedover a' wide frequency' range', suchgas from` 1-0' `to 3500 megacycles,'and rwhich -are supplied through a choke 2 to a first mixer orrfrequency converter'3.' Locally generated oscillations ofa frequencyvf2 considerably higher than the frequency fl -ofthe received signals,for example inthe vcentimeter Wave region, and varying' over a rangewhich is at least as broad (in magacycles) astherange of thereceivedlsignals, 'are' supplied `from' a "varie able frequency localoscillator 4 through a rejec` tion filter 5 to thev mixer or frequencyconverter 3. The converted output signals of the mixer 3, which aresignals of a constant, very highfrequency, are l suppliedfthrough asharply l tuned transmission [filter 6 to al'second mixer` or fre'-quency converter 1.' Local-oscillations are 4likewise supplied to the.mixer 'l'from a second local oscillator B'through afpa'irof.rejectionfilters9,4 I0. vThe frequency f3^of theoscillationsof theoscillator- 8 is' of yther isame order i'as-r that of vthe' oscillator4. It is separated from-the constant frequency output signal ofmixer-"3I by a fre` .In the' circuit of Figfi, the alters 5, t andiluare all tuned tothe frequency of theconstantf frequency` signalobtained" through the frequencyv conversion actionv of the mixer 3,kthat `is,fo'r example the'difference between the frequency 'of asiansme'gaeycles, arel mixed through the action vof the crystal -25withioscilla'tions from the source 4 to provide a constant frequencysignal. This constantI frequency signal is filtered by the transmissionfilter 6 -to 'removeundesired modulation products and 'suppliedtothecrystal 36 where it is mixed with'oscillationsfrom the source 8 toproduce a constant frequency output signal of relatively low lfrequencywhich-is supplied to theV amplifier I2. Th oscillator 4 is' variable incharacter and isVaried-"over its tuning range, which may be from 22,000to 25,500megacycles, until the mixed signal produced by the crystal 25is of the frequency to which the transmission filter 6 tuned;yWhen-thefrequencies of the source I andthe oscillator 4 are thuscorrelated, a constantultra high frequency signal is provided by crystal25. mission filter 6 and is combined by crystal 36 with oscillationsfrom voscillator-8. These oscillations are of ultra'high frequency, forexample 21,885 megacycles. The crystal 36combines the two ultra highfrequency waves to form a con-k stant low frequency signal'which issupplied over the transmission line 38, 39 -to the amplifier l2 so thatan indication is obtained on the cathode ray tube i3 vor anyothersuitable output device. The rejection filter reflects the constantfrequency signal obtained 'through the action of the crystal in properphase so that this signal is not lostl in the guide section connectingwith oscillator 4. but is transmitted efciently to element 36.Similarly, the rejection filter I0 vprevents transmis-v This signalpasses through transsion to the oscillator 8 of the constant frequencyvsignal transmittedthrough the transmission fllter 6 and permitsefiicientpickup and conversion by crystal 36.

The filter eshort-circuits the ventiou as applicable to an ultra'hignfrequenoy spectrum analyzer, it is apparent that the invene tion maybe employed to analyze lower frequency waves?, one of the requirementsbeing the use of an oscillator variable over afrequency 'rangeof cyclesor kilocycles equal to the range of fre-1 quencies to be covered by theanalyzer. `It isapparent likewise thatwhenl used for lower fre'-quencies the filters of thesystem which are employed may be different inform from those illustrated in the gures of the drawing; Furthermore, bythe use of suitable pretuning circuits before supplying an input wavetoa rstmixer of the analyzer, further rejectionv of undesired signals isobtained. While I have shown and described my invention by reference toa particular embodiment thereof, it will be understood that numerousmodifications may be made by those skilled in the art without departingfrom' the invention. I therefore aim in the appended claimsto coverallsuch equivalent variations as come within the v-true spirit and scope ofmy invention. y

What I claim as new and desire to secure 4by Letters Patent of theUnited States, is:

1. Apparatus for determining `the frequency of an ultra high frequencywave comprising a metallic Wave guide of the hollowpipe type, a pair ,of0S.- cillators connected respectively to opposite ends of said guide forsupplying thereto oscillations of a frequency substantially larger thanthe frequency of said wave, a pair of nonlinear devices connected acrosssaid guide at spaced points, filftering means comprising a cavityresonator pof- Vsitioned vtransverse said guide between -said points,said resonator having apertures cornf municating with said guide onopposite sides of crystal36 for undesired modulation products of Icrystal 25 that leak through filter 6.

- From the foregoing explanation, it is seen that an important advantageof my spectrum analyzer is that it allows the detection of inputfrequencies over a wide range and simply through the tuning of theoscillator 4 alone, which may be effected by a simple tuning knob,supplies to the amplifier l2 a constant frequency signal. At the sametime,

undesired modulation products which might otherwise produce spuriousresponses are suppressed through the filtering action of the filters 5,t, 9, and i0. It is thus apparent that a single full strength responsefor a given input signal is obtained if the oscillator 4 is tunedthrough its complete range, all other responses requiring at least a 30db. larger input. Another advantage of my invention is that the nltersrequired are simple in character and at the high frequencies employed,are quite sharp in action and have a high Q.

It is well known that in frequency conversion apparatus utilizingcrystals as a frequency converting medium, the crystals must be operatedunder eicient conditions in order to prevent loss of received signals.To that end it is essential that proper termination of the wavetransmitting channel be provided for the various frequency waves presentin the crystal circuits. This is achieved in my improved circuits bymeans of the filters 5, 6, 9, and l0 and by means of the chokes 2 and H,which so terminate the respective portions of the wave transmissionchannel that no received energy is dissipated through impropertermination. As a result, good conversion efficiency is obtained in eachof the crystals 25, 36.

While in the foregoing I have described my insaid resonator, means forsupplying said wave to said guide on one side of saidltering means, andoutput means connected to `said guide on the other side of saidfiltering means.

2. An ultra high frequency receiver comprising a metallic wave guide ofthe hollow pipe type, a pair of oscillators connected respectively toopposite ends of said guide forsupplying thereto oscillations of afrequency substantially larger than the frequency of a received wave, apair of nonlinear devices connected across said guide at spaced points,filtering means comprising a cavity resonator positioned transverse saidguide between said points, said resonator having apertures communicatingwith said guide on opposite sides of said resonator, means supplyingsaid wave to said guide on one side of said filtering means, outputmeans connected to said guide on the other side of said filtering means,and additional cavity resonators connected across said guide betweeneach of said nonlinear devices and the one of said oscillators adjacentthereto.

3. A receiver for high frequency signals varying .over a wide range ofhigh frequency comprising a metallic wave guide of the hollow pipe type,a first source of oscillations of a frequency higher than the frequencyof said signals connected to said wave guide at one end thereof, meansfor supplying received signals to said guide at a point adjacent saidone end, means for combining said received signals with saidoscillations to produce a converted signal of constant high frequency, asecond source of oscillations having a frequency of the order of thefrequency of said first oscillations connected to said wave guide at itsother end, means including a cavity resonator connectcd across saidguide between said converting .ames

f7 Ineens and said second source for removing'nundesired modulationproducts 4from said converted signal, and means for combining saidconverted signal with said second oscillations to produce a secondconverted Vsignal of lower constant frequency.

4. A receiver for signals varying over a Ywide range'of ultra highfrequencies comprising a metallic wave guide of the hollow pipe type, afirst-source of oscillations of a frequency higher than any frequency insaid range connected to one end of said guide, the frequency of saidfirst source being variable over a. second range equal in width to saidfirst range, a second source of constant frequency oscillations of afrequency higher than any frequencyl of said rst rangeconnected to saidguide at its other end, filtering means comprising a cavity resonatorpositioned transverse said guide at a point between said ends, saidresonator having apertures communieating. with said guide lon oppositesides of said resonator,l means for supplying said signals to saidguideat a point between said filtering means md'said first source',mixing means connected across said guide between said ltering means andsaid .nrst source to combine said signals and oscillations of said firstsource to produce a constant frequency wave, said filtering means beingtuned to the frequency of said wave, a second mixing means connected tosaid guide between said filtering means and said second source toproduce a constant. frequency output signal determinedby the frequencyof said wave and oscillations of said second source, and output meansconnected to said guide between said filtering means and said secondsource. l n

5. A receiver for signals varying over a wide range of ultra highfrequencies comprising a wave guide of the hollow pipe type, a variableoscillator connected to said guide at one of its ends andla Constant.frequemaosciilatorconnected t0 laid ,guide .at its other end,,fi-11st.l ltering means comprising a cavity l:resonatorpositionedtransverse said guide at al point between said ends, said resonator.havingl apertures communicating `with said guide onoppositesidesof.said resonator, .means ,for suppblingfsaid signalsfto said guide betweenIsaid variable oscillator A and said filtering means, a flrstrcrystal;rectifier connectedacross saidlguide for. 'mixing Lvsaid oscillationsfrom said :variable -oscillatorand saidvsignals to produce a constantfrequencyvwave, said filtering means be- ,ing tuned to thefrequencyoisaid wave, a second lcavity resonator connected between said firstcrystal rectifier .and said variable oscillator to prevent loss Aof saidwave, atecoxiel` crystal rectifier connected-between said. :firstfiltering means and said constant fiequencyoscillator to produce anoutput signal determined by the frequency oi said wave and ksaidconstant frequency oscillations, a third cavity resonator connectedbetween said second crystal rectier and s aidconstant frequencyoscillator to`A prevent said wave from reaching said constant frequencyoscillator, and output electrodey means connected to said guide betweensaidiirst andftliird cavity resonators. i l LE ROY APKER.

v REFERENCES CITED. The following vv referencesfare" lo1' record'ln theiile of vthis. patenti' i UNITEDVA s'rn-'rissr PATENTS n 2,378,944 Ohl i..-v June 26, 1945

